The present invention relates to instantaneous water heaters and, more particularly, to a method and apparatus for accurately controlling the output water temperature of an instantaneous water heater.
Typically, most buildings, both houses and commercial, are built with heating sources for domestic hot water. This includes energy conversion units and distribution systems, largely tank type storage units, namely gas or oil burners or electric elements; sets of controls, namely thermostats, thermocouples, electric valves and regulators; hot water storage tanks and heat exchangers; and conduits for transferring the heated water. All of these components result in an unduly large system required for heating water.
Such large systems tend to be inefficient and inconvenient in large homes or buildings, and entirely impractical for vacation cabins, land and water based recreational vehicles, house trailers, firemen's hazardous material decontamination units, and military field water uses, all of which have limited space and weight and require their own independent water sources as distinguished from those using common water supplies of municipalities.
In situations where space is at a premium, it has been the general practice to provide a liquid or gaseous hydrocarbon tank type water heating unit having a very low water capacity and heating capacity. Although the unit satisfies the requirement of compactness, the low capacity places limits on bathing and other hot water usage. Another problem associated with tank type water heaters is rather low efficiency and standby heat loss. The result is higher energy use. When water is heated and stored, heat loss from the tank occurs and the water has to be re-heated to the appropriate temperature.
One solution, in situations where water is readily available, is to use a tankless, on-demand water heater to provide hot water. Such a heater conserves space and produces higher quantities of hot water when compared to the comparable sized tank type heater. These systems tend to be more energy efficient because tank stand-by heat loss is eliminated. Unfortunately, a problem which exists with instantaneous water heaters is maintaining precise temperature control with varying flow rates and varying incoming ambient water temperatures. Wide temperature fluctuations occur as additional water taps are opened or closed. Obviously, poor control of water temperature can create negative responses from users, from mild annoyance to actual safety hazards. For example, fluctuations in hot water temperature can cause burns to bathers during a shower, and to small children using hot water.
It is seen then that there exists a need for a system and method for heating water which can precisely control output water temperature, even with varying flow rates and varying incoming ambient water temperature. It would also be desirable to have such a system and method which eliminates some of the troublesome mechanical components of current instantaneous water heaters. Finally, it would be desirable to have such a system and method which has a higher heating capacity, giving it the ability to precisely control large heat exchangers at low water flows.